1. Field of the Invention
The present invention relates to an image forming device.
2. Description of the Related Art
Conventionally used image forming devices include what we call ink-jet image forming devices that discharges ink droplets through a nozzle of a recording head. Japanese Patent Application Laid-open No. 2005-225207 (hereinafter called “Patent Document 1”) discloses a type of the ink-jet image forming devices. The ink-jet image forming device disclosed in Patent Document 1 performs preliminary discharge of ink droplets through the nozzle in the absence of sheets in order to prevent problems such as attachment of foreign substances to the nozzle of the recording head, which may result in ink jam, defect in the amount of discharge, defect in a recording position (direction in which ink is discharged), etc. The aforementioned preliminary discharge allows removal of the foreign substances attached to the nozzle.
In the image forming device disclosed in Patent Document 1, ink droplets are discharged toward a large number of through holes (suction holes) defined in a transport belt, and pass through the through holes during the preliminary discharge. That is, in the preliminary discharge, ink droplets are discharged through nozzles overlapping the through holes, thereby preventing attachment of ink droplets to the transport belt to be caused as a result of the preliminary discharge. Furthermore, while the transport belt is caused to circulate, ink droplets are discharged through every nozzle in the preliminary discharge by sequentially changing nozzles to be used to discharge ink droplet as nozzles overlapping the through holes change.
When deformation (such as stretch or contraction) is generated in the transport belt as a result, for example, of its exhaustion, the positions of the through holes are changed from their initial positions at the start of use of the image forming device. Accordingly, if the timing of preliminary discharge is the same as that of an initial stage at the start of the use, ink droplets may attach to the transport belt. In order to avoid this, in the conventional image forming device, the range into which ink is discharged is set narrower with respect to the size of the through holes. By doing so, ink droplets do not attach to the transport belt even when the through holes slightly shift from their initial positions as a result, for example, of deformation of the transport belt.
However, narrowing the range into which the preliminary discharge is performed with respect to the size of the through holes reduces the number of nozzles through which ink droplets are discharged to each of the through holes at a time in the preliminary discharge. This in turn requires longer time in completing the preliminary discharge through every nozzle.